Chapter
1. INTRODUCTION AND PROJECT HISTORY

The Federal Highway Administration (FHWA) research project,
Corrosion Resistant Reinforcing for Concrete Components,
began in 1993. The objective of the proposed study was to develop
cost-effective new breeds of organic, inorganic, ceramic, and
metallic coatings, as well as metallic alloys that could be
utilized on or as reinforcement for embedment in portland cement
concrete. It was required that new coatings and alloys should
provide significantly more corrosion-resistant reinforcement than
the fusion-bonded epoxy-coated reinforcement that has been used in
the United States since 1975 and also the corrosion-free design
life shall be 75 to 100 years when exposed to adverse
environments.

The research was aimed at developing new reinforcement materials
and systems that minimally damage the coating system during (1)
coating application, (2) fabrication bending operations, and
(3) shipment to and installation at the jobsite. It was required
that alloys have superior characteristics, and that thin-clad
conventional steel resist damage. The coating systems had to have
superior physical and chemical properties that remain undamaged by
long-term exposure to ultraviolet radiation, high temperatures,
salt-laden atmosphere, and other environmental conditions during
long-term storage before casting them in concrete.

On March 3, 1993, 3M informed the researchers that Scotchkote
213 (3M 213TM ) would no longer be manufactured, because
of rulings from the U.S. Environmental Protection Agency (EPA). The
3M 213 epoxy-coated bars had been used almost exclusively in the
bridges in the United States from about 1980 to 1990. Based on this
change, it became crucial to secure bars coated with the 3M 213 for
the in-concrete tests that were to begin in 1995.

An invitational letter for submitting candidate bars was sent to
46 companies on May 17 and 18, 1993. It was anticipated that
numerous new candidate organic coatings would be submitted for
testing, because the 3M 213 epoxy coating material was no longer
available, and new steel surface pretreatments used before coating
the bars were being considered. As a result, researchers used a
30-day prescreening test program to screen these numerous
organic-coated candidate bar systems, with and without special
steel surface pretreatments. At that time, the organic coaters
agreed that pretreatment would improve coating adhesion strength
and long-term performance.

Prescreening tests on organic-coated bars were conducted from
1993 to 1995. These screening tests are chronicled in two reports:
The Performance of Bendable and Nonbendable Organic Coatings for
Reinforcing Bars in Solution and Cathodic Disbondment Tests[1] and the related phase II screening test
report.[2] Screening tests were also conducted from 1993
to 1995 on metallic-clad and solid metallic bars. This research
studied 10 types of metal clad bars and 10 types of solid
metal bars. The performance of various inorganic-, ceramic-, and
metallic-clad bars and solid corrosion-resistant bars is discussed
in the 1996 FHWA report, The Corrosion Performance of
Inorganic-, Ceramic-, and Metallic-Clad Reinforcing Bars and Solid
Metallic Reinforcing Bars in Accelerated Screening
Tests.[3]

Based on screening tests as detailed in the three reports
mentioned above, 12 bar types were selected for the 96-week
in-concrete testing. The 141 reinforced concrete slab specimens
using 12 different bar types were made and were exposed to the
96-week SE testing. These tests were completed in late 1997, and
the final report was published in a 1998 FHWA report, Corrosion
Evaluation of Epoxy-Coated, Metallic-Clad and Solid Metallic
Reinforcing Bars in Concrete.[4]

The 96-week SE testing involved with the following wetting and
drying cycles:

The 15 percent salt solution was chosen to represent the high
salt concentrations occurring on inland bridge structures from
deicing salts. The long ponding period was utilized to simulate a
sustained period of submersion or long periods of high concrete
moisture common in winter months or in marine structures. This
24-week cycle was repeated four times for a total test period of 96
weeks.

Configuration of the concrete slabs used in this FHWA study
measured 30.5 x 30.5 x 17.8 centimeters (cm) (12 x 12 x 7
inches) and contained two layers of 29.2-cm (11.5-inch) long and
1.6-cm (5/8-inch) diameter reinforcement, as shown in figure 1. The
top mat acted as a macroanode and contained either two straight or
two bent reinforcing bars, while the bottom mat was a macrocathode
that contained four straight reinforcing bars. The top mat bar was
connected to two bottom mat bars through a 10Wresistor. A clear
cover of 25.4 millimeters (mm) (1.0 inch) was used in all
specimens. This cover conforms to either the American Association
of State Highway and Transportation Officials- (AASHTO) specified
bottom-of-slab cover, or possible minimum in-place clear cover,
allowing for construction tolerances when 3.8- to 5.0-cm (1.5- to
2.0-inch) cover requirements are specified. While most previous
published corrosion studies used only crack-free concrete slabs,
some of the test slabs used in this project contained the cracks
directly over a top mat rebar to simulate cracks observed on actual
bridge decks. Table 1 presents the concrete mix design data for the
test slab concrete.

1 inch = 25.4 mm

Figure 1.
Configuration of test slab

Table 1. Mix properties
of concrete used

Concrete Property

Mean Value of 30 Batches

Standard Deviation

Cement, kg/m3 (lb/yd3)

370 (623)

3.3 (5.56)

Air, percent

5.6

0.51

Slump, mm (inch)

167 (6.58)

31.7 (1.25)

Unit wt., kg/m3 (lb/yd3)

2315 (144.5)

21.0 (1.31)

w/c

0.47

0.01

28-day compressive strength, MPa (psi)

39.3 (5,700)

2.7 (403)

Table 2 shows the chloride concentration data collected during
the 96-week FHWA study, and figure 2 shows the estimated chloride
concentration at the top mat depth (2.5 cm or 1.0 inch) with time.
It is clear that rapid migration of chloride is achieved through
the SE testing. At the sixth week of testing, chloride
concentration at the 2.5 cm (1.0 inch) depth exceeded2.97
kg/m3 (5 pounds (lb)/yard (yd)3) (0.137
percent or 1,370 parts per million (ppm)), which was greater than 3
times the known chloride threshold (0.71 to 0.89 kg/m3
(1.2 to1.5 lb/yd3) or 300 to 350 ppm) for uncoated
American Society for Testing and Materials (ASTM) A615 bar.

Table 3 summarizes the performance data of seven different rebar
materials tested under the 96-week FHWA test program. Figures 3 and
4 show average macrocell current and mat-to-mat AC resistance data
of each type reinforcing bar in table 3. Furthermore, table 4
classifies average macrocell current and mat-to-mat AC resistance
of the ECR slabs for each coating type. The 96-week FHWA study
concluded that the best ECR performance was obtained when the bars
were tested in a straight condition, with 0.004 percent damage in
uncracked concrete using an ECR cathode in the bottom mat.
Researchers also found that there was a clear relationship between
the mat-to-mat resistance values of the ECRs and their corrosion
performance. Better corrosion protection was provided by those
coating systems that had high electrical resistance, that is, the
corrosion was strongly dependent on the amount of damage in the
coating.[4]